Loren Howard, Neely Odom and Joseph DuBose (left to right) participate in a lesson on gender diversity at Redwood Heights Elementary School in Oakland, Calif. on Monday, May 23, 2011. The students were given cards describing gender differences in nature and then asked to read the cards aloud for the class.

Photo: Laura Morton, Special To The Chronicle

Loren Howard, Neely Odom and Joseph DuBose (left to right)...

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Students at Redwood Heights Elementary School look over cards describing gender differences in nature during a lesson on gender diversity in Oakland, Calif. on Monday, May 23, 2011. The students were given cards describing gender differences in nature and then asked to read the cards aloud for the class.

Photo: Laura Morton, Special To The Chronicle

Students at Redwood Heights Elementary School look over cards...

Image 3 of 3

Joel Baum, the director of education and training for the organization Gender Spectrum, teaches a lesson on gender diversity to students including 9-year-old Loren Howard (left) and 10-year-old Clemente Ferrer at Redwood Heights Elementary School in Oakland, Calif. on Monday, May 23, 2011.

A one-hour elementary school lesson on gender diversity featuring all-girl geckos and transgender clownfish caused a stir in Oakland on Monday, with conservative legal defense organizations questioning the legitimacy of the topic and providing legal counsel to parents who opposed the instruction.

On Monday and today, Redwood Heights Elementary School students at every grade level were being introduced to the topic of gender diversity, with lesson plans tailored to each age group.

The lesson on gender differences was one small part of a much larger effort to offer what parents last year said they wanted at the school: a warm, welcoming, safe and caring environment for all children, said Principal Sara Stone.

The school also teaches students about the variety of families at the school and takes on the issue of bullying.

"If we don't have a safe, nurturing class environment, it's going to be hard to learn," she said. "Really, the message behind this curriculum is there are different ways to be boys. There are different ways to be girls."

So, fourth- and fifth-grade students learned about the crazy world of gender within the animal kingdom with lessons about single-sex Hawaiian geckos, fish that switch genders and boy snakes that act "girly."

"That's a lot of variation in nature," Gender Spectrum trainer, Joel Baum, told the students. "Evolution comes up with some pretty funny ways for animals to reproduce."

Animals and people

And that same kind of diversity applies to people too, said Baum, the education director for the San Leandro nonprofit. For example, some boys can act like girls; some girls can have boy body parts; and some biological boys feel like a girl inside their hearts, he said.

A requirement

All state schools are required to have a specific plan to address safety and other issues related to sexual orientation and gender identity.

"Gender harassment can start at very young ages, often before kindergarten, and it is not uncommon for children who step outside of narrow gender expectations, whether in their clothing, hair, toys or styles of play, to become the targets of mistreatment by other children," said district spokesman Troy Flint in an e-mail.